泛型对象可以实例化吗？

不可以，T t=new T()是不可以的，编译器会报错。由于泛型擦除，编译器在编译时无法确定泛型所对应的真实类型

解决方法

使用反射新建实例

Type superclass = getClass().getGenericSuperclass();

ParameterizedType parameterizedType = null;

if (superclass instanceof ParameterizedType) {

parameterizedType = (ParameterizedType) superclass;

Type[] typeArray = parameterizedType.getActualTypeArguments();

if (typeArray != null && typeArray.length > 0) {

clazz = (Class) typeArray[0];

}

}

执行结果

控制台输出

完整代码

package com.learn.genericinstance;

import java.lang.reflect.ParameterizedType;

import java.lang.reflect.Type;

public class GenericInstanceLearn {

public static void main(String[] args) throws InstantiationException, IllegalAccessException {

UserDao userDao = new UserDao();

System.out.println(userDao.toString());

}

}

class Dao {

public Class clazz;

public T user;

public Dao() throws IllegalAccessException, InstantiationException {

Type superclass = getClass().getGenericSuperclass();

ParameterizedType parameterizedType = null;

if (superclass instanceof ParameterizedType) {

parameterizedType = (ParameterizedType) superclass;

Type[] typeArray = parameterizedType.getActualTypeArguments();

if (typeArray != null && typeArray.length > 0) {

clazz = (Class) typeArray[0];

user= clazz.newInstance();

}

}

}

@Override

public String toString() {

return "Dao{" +

"user=" + user.toString() +

'}';

}

}

class UserDao extends Dao {

public UserDao() throws IllegalAccessException, InstantiationException {

}

@Override

public String toString() {

return super.toString();

}

}

class User {

String name;

public User() {

this.name = "default name";

}

@Override

public String toString() {

return "User{" +

"name='" + name + '\'' +

'}';

}

}

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